This invention relates to an auto-focusing apparatus used for auto-focusing an image-pickup optical system such as an electronic image pickup apparatus.
In recent years, some of electronic image pickup apparatus (e.g. a video camera) using an image sensing element are provided with an auto-focusing function to automatically focus an image pickup optical system at a focal position on the basis of the output of the image sensing element.
There has been developed an auto-focusing apparatus employing hill-climbing method or full-scanning method.
According to the hill-climbing method, an optical system can be easily focused at a focal position with high precision when the subject is bright. When the subject is dark, however, it is difficult to focus an optical system at a focal position with high precision.